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8/13/2019 Endodontically Treated Tooth
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Influence of adhesive techniques onfracture resistance of endodonticallytreated premolars with various residualwall thicknesses
Nicola Scotti, DDS,a RiccardoRota, DDS,b Marco Scansetti, DDS,c
Davide Salvatore Paolino,ING,d Giorgio Chiandussi, ING,eDamiano Pasqualini, DDS,f and Elio Berutti, MD, DDSg
Dental School Lingotto, University of Turin, Turin, Italy; Politecnico diTorino, Turin, Italy
Statement of problem. The choice of restorative method is commonly based on the cavity conguration and the residualnumber of cavity walls. However, the residual wall thickness could be a valuable clinical parameter in the choice of restorationfor endodontically treated teeth.
Purpose.The fracture resistance of endodontically treated premolars was compared with different wall thicknesses restored
with direct composite resin with and without cuspal coverage and with and without
ber post insertion.
Material and methods.This study included 104 intact human maxillary premolars extracted for periodontal or orthodonticreasons. Standardized mesio-occluso-distal cavities were prepared with different palatal wall thicknesses (1.5, 2, and 2.5 mm)and a buccal wall thickness of 2 mm. Teeth were restored with or without a ber post and with or without cuspal coverage.Specimens were subjected to thermocycling (3000 cycles, 5 to 55C) and embedded in polymerized acrylic resin. Teeth weresubmitted to cyclic fatigue followed by a static fatigue test with a universal testing machine; a compressive force was applied30 degrees to the long axis of the teeth until fracture. The results were statistically analyzed by 3-way ANOVA ( a.05).
Results. Residual wall thickness (P.004), the type of adhesive restoration (P
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loss. Of the various post systems avail-
able, metal orber posts are commonly
recommended for clinical use.5 The
introduction of adhesive techniques
and the use of ber-reinforced posts
in conjunction with composite resin
foundation restorations have facilitated
the preservation of tooth structure.6
Moreover, if the post and core havethe same elastic modulus as root
dentin, forces will be distributed along
the long axis of the post, improving the
fracture resistance of endodontically
treated teeth in vitro.7-9 The function of
a ber post is to improve the retention
of the denitive restoration and to
distribute occlusal stressors along the
remaining tooth structure. Posts do
not strengthen endodontically treated
teeth,10,11 especially anterior teeth,12
although some studies have suggested
that cast metal posts result in reduced
stresses in the dentin.13
However, endodontically treated
teeth restored with direct techniques,
with or without posts, may sometimes
present residual compromised cusps
that could eventually fracture. In these
patients, reduction and coverage with a
complete crown is usually indicated to
prevent coronal fracture.14,15 However,
the concept of minimal intervention
dentistry to maximize preservation of the
tooth structure is gaining popularity in
the restoration of endodontically treated
teeth.13 Tooth structure preservation is
directly correlated with fracture resis-
tance,16,17 reducing the occurrence of
catastrophic failures and enhancing the
longevity of the restoration. In vivo and
in vitro studies support the use of
direct intracuspal adhesive techniques
for the restoration of endodonticallytreated teeth if a normal occlusion
without parafunction is present.18,19
This approach has the advantage of
reinforcing teeth without occlusal
coverage.20-22 To date, few prospective
clinical studies have evaluated the
different types of direct or indirect ad-
hesive restorations of endodontically
treated teeth. Mannocci et al23 found
ber posts and direct composite resin
restorations to be more effective thanamalgam in preventing root fractures,
but not secondary caries, of endodonti-
cally treated premolars. Another pro-
spective in vivo study24 showed similar
3-year survival rates between endodon-
tically treated premolars restored with
ber posts and direct composite resin
restorations and complete coverage with
metal ceramic crowns.
The thickness of the residual cavitywall could be a simple but effective
parameter for clinically evaluating the
remaining tooth structure and conse-
quently for the selection of the most
appropriate type of restoration for
endodontically treated teeth. However,
this parameter has not been investi-
gated extensively. The choice of restor-
ative method is commonly based on the
cavity conguration and the residual
number of cavity walls.25,26 However,
because the residual cavity wall thick-
ness represents the quantity of remain-
ing enamel and dentin and is directly
correlated with the residual sound tis-
sue,27 wall thickness evaluation could
provide more information to the clini-
cian regarding the fatigue resistance
of an endodontically treated tooth.
Therefore, the purpose of this in vitro
study was to evaluate the effect of
cavity wall thickness on the fracture
resistance of endodontically treated
teeth restored with a variety of adhesive
techniques. The null hypothesis tested
was that residual wall thickness does
not inuence the fracture resistance
or fracture mode of endodontically
treated premolars restored with or
withoutber posts and with or without
cusp coverage.
MATERIAL AND METHODS
After receipt of institutional board
approval, the study included 104 non-
carious single-rooted maxillary pre-
molars with mature apices recently
extracted for orthodontic or peri-
odontal reasons. The inclusion criteria
were an absence of restorations, similar
crown and root sizes, and no cracks
under transillumination. Selected teeth
were stored in 0.5% chloramine T tri-
hydrate at 4
C. After cleaning the toothsurfaces, endodontic treatment was
performed on all specimens except
those in the control group (intact teeth;
n8). Specimens were endodontically
instrumented with Pathles (1-2-3) and
ProTaper (S1-S2-F1-F2-F3) (Dentsply
Maillefer) to the working length,
enlarging the apex to a size 30, 0.09
taper. The specimens were irrigated
with 5% NaOCl alternated with 10%EDTA (ethylenediaminetetraacetic acid)
with a 2-mL syringe and 25-gauge
needle. Specimens were obturated
with gutta percha by using a heat
source (DownPack; Hu-Friedy) and an
endodontic sealer (Pulp Canal Sealer
EWT; Kerr Corp). Backlling was per-
formed with the Obtura III system
(Analytic Technologies).
After 24 hours, all specimens were
assigned to 3 groups (W1.5; W2; W2.5;
32 teeth each) based on the thickness
of the residual palatal wall (1.5, 2, and
2.5 mm) after cavity preparation,
measured with a caliber at the occlusal
oor of the cavity. The specimens were
treated as reported by Scotti et al.22 In
each tooth, a class II mesio-occluso-
distal cavity was prepared. In order to
compensate for different coronal anat-
omy, all teeth were prepared by hand by
1 experienced operator. The prepara-
tion was extended until the gingival
cavosurface margin was 1-mm coronal
to the cement-enamel junction. The
residual thickness of the buccal cusps at
the height of the contour was 2 0.2
mm. Within each group, the specimens
were further randomly assigned to 4
subgroups (8 teeth each) on the basis
of the restoration type (Table I). In the
groups with cusp coverage (overlay),
both cusps were reduced with a
completelyat enamel margin of up to2 mm.
In the ber post groups, the post
space was prepared with drills from the
post manufacturer (Dentsply Maillefer)
to a depth of 7 mm, measured from the
pulpal chamber oor. All adhesive
procedures were performed with All-
Bond 3 (Bisco) according to the man-
ufacturers instructions. For ber
post cementation, a dual-polymerizing
cement (NanoCore Dual; Dentalica)was used. Dual-polymerizing cement
November 2013 377
Scotti et al
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was applied into the canal by using a
tube with a needle and the appropriate
plug (KerrHawe SA) and by injecting
the materials into the post spaces with
a specic Composite-Gun (KerrHawe
SA). Size 1 RTD ber posts (RTD) were
cemented to the full depth in the
prepared post spaces. After initial
preparation, photopolymerization wasperformed with an LED-polymerization
light for 40 seconds (Translux; Heraeus
Kulzer) at 1200 mW/cm2.
After xing the matrix band with a
retainer, A2-shaded nanohybrid com-
posite resin (Venus Diamond; Heraeus
Kulzer) was placed by using an oblique
layering technique. Each layer, 1.5 to
2 mm thick, was polymerized for 20
seconds with an LED-polymerization
lamp at 1200 mW/cm
2
(Translux Po-wer Blue; Heraeus Kulzer). The matrix
band and retainer were then removed,
and postpolymerization was performed
on the buccal and lingual aspects of the
boxes for 40 seconds on each side. All
the restored specimens were nished,
polished, and then stored in distilled
water at 37C for 7 days. All specimens
were subjected to 3000 thermal cycles
between 5 and 55
C for 60 secondseach. All specimens were embedded in
light-polymerizing acrylic resin to 1 mm
below the cement-enamel junction,
with a thin layer of polyvinyl siloxane
(Aquasil; Dentsply Italia) around the
root to simulate the periodontal liga-
ment. Specimens were then exposed to
cyclic loading (Mini Bionics II; MTS
Systems) with an inclination angle of 30
degrees to the long axis of the tooth
and at a frequency of 8 Hz, startingwith a load of 20 N for 5000 cycles,
followed by a stage of 50 N for 20 000
cycles. A 10-mm-diameter metal ball
was used. The site of loading was the
central ssure of the occlusal surface of
the restoration in the direction of the
buccal cusp. The specimens were then
submitted to the static fracture resis-
tance test by using a universal testing
machine (Instron) with a 2-mm-diam-eter steel sphere crosshead welded to
a tapered shaft and applied to the
specimens at a constant speed of
2 mm/min and at an angle of 30 de-
grees to the long axis of the tooth. The
forces necessary to fracture each tooth
were measured in newtons (N).
Restorable and nonrestorable frac-
tures were distinguished by using an
optical stereomicroscope with agree-
ment by 2 examiners. Restorable fail-ures included fractures above the
Table I. Specimen characteristics, grouping, mean fracture resistance values (Newtons), and fracture modes ofvarious groups
Group
(n[32)
Residual Wall
Thickness
Subgroup
(N[8) Characteristics
Fracture
Resistance
(mean SD)
Nonrestorable
Fracture (%)
W1.5 1.5 mm W1.5 A Post (-), cuspcoverage (-)
260.51 82.69 87.5
W1.5 B Post (), cuspcoverage (-)
445.71 103.19 62.5
W1.5 C Post (-), cuspcoverage ()
793.11 196.56 87.5
W1.5 D Post (), cuspcoverage ()
775.98 173.30 87.5
W2 2 mm W2 A Post (-), cuspcoverage (-)
313.77 69.61 75
W2 B Post (), cuspcoverage (-)
660.59 149.48 50
W2 C Post (-), cusp
coverage ()
801.16 175.28 87.5
W2 D Post (), cuspcoverage ()
868.58 139.76 87.5
W2.5 2.5 mm W2.5 A Post (-), cuspcoverage (-)
368.22 130.27 87.5
W2.5 B Post (), cuspcoverage (-)
676.06 155.56 50
W2.5 C Post (-), cuspcoverage ()
821.18 121.45 75
W2.5 D Post (), cuspcoverage ()
871.77 150.74 87.5
Control(n8)
- - Intact teeth 1098.64 287.86 20
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The Journal of Prosthetic Dentistry Scotti et al
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cement-enamel junction, meaning that
the tooth could be restored even in in-
dividuals with major coronal tissue loss.
Nonrestorable failures included fracture
patterns that extended below the
cement-enamel junction, in which a
surgical approach would be required to
perform an adhesive restoration.
A statistical analysis of variance(3-way ANOVA, including 2-way and
3-way interactions, a.05) was per-
formed to evaluate the inuence of the
residual wall thickness (factor T at
levels 1.5, 2, and 2.5 mm), the resto-
ration (factor R at inlay and onlay
levels), and the ber post (factor P at 2
levels) on the fracture resistance of the
tooth. A c2 test was used to compare
the failure modes of the specimens.
Differences were considered statistically
signicant at values ofa.05.
RESULTS
The mean fracture resistance values
and the modes of failure observed in
the groups are listed in Table I. The
normal probability plot showed that
the residuals followed a normal distri-
bution. None of the tested restorations
showed similar fracture resistance
values to the control group, even
those with residual walls of 2.5 mm.
Within the restored specimens, ANOVA
(Table II) showed that the thickness of
the residual wall (P.004), the type of
adhesive restoration (P
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treated premolars. Regardless of wall
thickness and post placement, teeth
with cusp cupping (factor restoration
at level onlay) showed the greatest
fracture resistance.
The c2 test showed statistically sig-
nicant differences in the patterns
of fractures between the subgroups
(c2
18.133; P
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undergoing root canal treat-
ment.10,13,27,39 According to Aquilino
and Caplan,13 although ceramic or
composite resin onlays could protect
against fractures, no reports support
their use in the restoration of posterior
teeth. Some in vitro studies concluded
that endodontically treated teeth
recovered the lost resistance to fractureafter receiving an indirect restoration
with cusp protection.22 The tendency of
onlay composite resin restorations to
receive higher load might be attributed
to the dispersion of compressive
stresses. Similar results were found for
cusp coverage with amalgam,39 which
signicantly increased the fracture
resistance of the teeth compared to
those restored without cusp coverage.
In contrast to the study by Soares
et al,40 cuspal reduction restorations
reduced fracture resistance in mandib-
ular premolars, probably because of the
large amount of sound tooth tissue
removed during specimen preparation.
Other authors have stated that cusp
coverage does not strengthen premolars
restored with composite resin onlay32
or molars with ceramic restorations.41
This may be due either to the different
axial direction of the compressive load
used in these studies, or to the different
indirect restoration, which involved
only a buccal cusp. Moreover, in this
study, the insertion of a ber post
within the cuspal coverage restoration
did not signicantly increase fracture
resistance, probably as a result of the
adequate dispersion of compressive
stresses already provided by the com-
posite resin overlay.21,26,30
Regarding failure mode, the combi-
nation of the ber post with an inlayadhesive restoration led to a higher
incidence of more favorable failure
types (P2 mm, less
invasive treatments such as direct in-
tracuspal composite resin restoration
supported by ber-post insertion can
provide sufcient fracture resistance to
occlusal loads. In contrast, when the
residual wall thickness is
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19. Yamada Y, Tsubota Y, Fukushima S. Effect of
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Corresponding author:
Dr Nicola Scotti
Via Nizza 230, 10100 Turin
ITALY
E-mail:[email protected]
Copyright 2013 by the Editorial Council for
The Journal of Prosthetic Dentistry.
82 Volume 110 Issue 5
The Journal of Prosthetic Dentistry Scotti et al
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